A basic magnesium carbonate that has been industrially utilized is represented by the chemical formula of mMgCO3.Mg(OH)2.nH2O. The value represented by m and n in this chemical formula varies depending on the condition of the production, and thus is not constant. It is common that m is 3 to 5, and n is 3 to 8.
The basic magnesium carbonate is usually obtained as amorphous aggregated particles of flaky fine crystals, having characteristics that a bulk density is as low as 0.2 to 0.3 g/mL, and a specific surface area is comparatively high and is 10 to 40 m2/g.
Basic magnesium carbonate has been utilized in the field such as rubbers, paints, paper manufacturing, medicinal products, cosmetics, building materials and ceramic materials through taking advantages of the characteristics as described above. Particularly, as a filler for a rubber, it has characteristics such as imparting transparency to a compounded natural rubber and improving the strength of a rubber.
As the method of producing a basic magnesium carbonate, there are many methods such as a soda ash method in which a reaction of a soluble magnesium salt such as magnesium chloride with sodium carbonate is utilized, an ammonium carbonate method in which a reaction of a soluble magnesium salt with ammonium carbonate is utilized, and a gas method in which a reaction of magnesium hydroxide with a carbon dioxide gas is utilized. In any one of these methods, production of a basic magnesium carbonate is allowed by a maturation for a long period of time of a normal magnesium carbonate (represented by the chemical formula of MgCO3.nH2O, wherein n is 3, in general) or magnesium bicarbonate (Mg(HCO3)2) obtained as an intermediate product by a reaction of a magnesium source with a carbonate source.
Investigation and development regarding the basic magnesium carbonate have been carried out since a long time ago. For example, a method for producing a basic magnesium carbonate having an excellent performance as a filler for use in a rubber within a short time through maturation of a suspension containing normal magnesium carbonate under an appropriate condition of the temperature was proposed in Japanese Patent No. 1207124, and a method for producing a basic magnesium carbonate having an excellent performance as a filler for use in a synthetic resin by a reaction of a water soluble magnesium source with a water soluble carbonate salt in the presence of a water soluble sulfate salt was proposed in JP-A-61-31314.
Further, a basic magnesium carbonate having a particular amount of oil absorption and specific surface area which is obtained by heating an aqueous solution of magnesium bicarbonate while circulation was proposed in JP-A-2-208220; and a basic magnesium carbonate exhibiting a particular X-ray diffraction pattern obtained by heating a suspension of normal magnesium carbonate in the coexistence of hydroxycarboxylic acid was proposed in JP-A-3-97618. Moreover, as the publications in which attention was focused on particle shape of a basic magnesium carbonate, there are Japanese Patent Nos. 1635418 and 2602444, where a basic magnesium carbonate in the form of a spherical porous particle formed by aggregation of primary particles, and which exhibits a feature such as a particular bulk density and a specific surface area was proposed.